First-trimester screening is a diagnostic test performed early in pregnancy. It is used to assess risk factors and potential conditions. Specialists in prenatal diagnostics advise expectant parents on how to prepare for, undergo, and interpret the possible results of a first-trimester screening.
Here you will find further information as well as a selection of specialists in first-trimester screening.
First-trimester screening is an examination of the mother and her unborn child early in pregnancy. During this screening, the doctor evaluates various factors that can help determine the risk of
- birth defects,
- chromosomal abnormalities, and
- pregnancy-induced hypertension, such as preeclampsia,
.
First-trimester screening should be distinguished from invasive diagnostics. “Invasive” means that a procedure is performed. Examples of invasive tests include amniocentesis and chorionic villus sampling. Unlike invasive methods, first-trimester screening is non-invasive and carries no risk of miscarriage.
However, first-trimester screening alone is not sufficient to rule out or diagnose a chromosomal abnormality. The doctor merely calculates the risk. Actual confirmation is only possible through invasive diagnostic procedures.
Parents who decide to undergo first-trimester screening should be aware that the results may lead to difficult decisions. Therefore, a detailed medical consultation beforehand is important.
First-trimester screening also includes an ultrasound © TommyStockProject | AdobeStock
When is first-trimester screening performed?
The screening takes place at the end of the first trimester. The time frame during which the tests can be performed is limited to the 12th to 14th week of pregnancy.
This is primarily due to the specific requirements of the nuchal translucency measurement. This test can only provide relevant results during this timeframe.
First-Trimester Screening Examinations
The screening involves a detailed ultrasound examination. During this procedure, the doctor measures and evaluates, among other things, the nuchal translucency thickness and the organs of the unborn baby.
About half of all serious birth defects can already be detected at this stage of pregnancy. To assess the risk of pregnancy-induced hypertension, the blood flow to the uterus is evaluated via ultrasound, among other methods.
Next, a blood sample is drawn from the pregnant woman. This allows for the determination of various laboratory values. A blood pressure measurement can also provide valuable information.
A few days later, the results are available, and the obstetrician discusses them with the pregnant woman.
Interpretation of the Results
The results of these tests are reported as a risk ratio. The risks can range from 1 in 2 to 1 in several thousand.
If the risk of chromosomal abnormalities is greater than 1 in 150, the obstetrician will recommend further testing. This could include, for example, amniocentesis.
If the risk is just below this threshold, additional ultrasound examinations or another blood test may be advisable.
The risk of pregnancy-induced hypertension is calculated in the same way. If the value is elevated, the obstetrician will discuss the daily use of aspirin.
Nuchal Translucency Measurement
What does nuchal translucency indicate?
Nuchal translucency thickness is an important criterion in assessing the risk of
- chromosomal abnormalities and
- malformations.
Every fetus has a fluid-filled space at the back of the neck. This is usually about 2 mm thick. A larger fluid-filled space increases the risk of chromosomal abnormalities and birth defects.
Other indicators of trisomy 21 include
- a shortened nasal bone and
- abnormal blood flow to and within the heart.
It is important to note that these markers do not constitute birth defects. Nor does an increased risk of chromosomal abnormalities equate to a developmental disorder. It is merely an indication that requires further investigation.
In fact, the majority of children with an increased risk develop normally.
For example, with a risk of 1 in 20, only one out of 20 fetuses in the same situation is affected, while the other 19 are normal. However, based on the determined risk, a joint decision can be made as to whether and which further tests might be appropriate.
What are the implications of the first-trimester screening results?
If there is an increased risk of chromosomal abnormalities, the expectant parents must consider whether further testing is advisable or not.
These include, for example,
- a detailed ultrasound examination in the 21st week of pregnancy,
- a cell-free DNA analysis from the mother’s blood, or
- an invasive diagnostic procedure such as amniocentesis or chorionic villus sampling.
The key factor is how the couple would respond to an abnormal result. The parents must decide whether they would terminate the pregnancy if an abnormal result were found. This requires appropriate specialized counseling from the obstetrician or psychosocial counseling services.
Who covers the costs of first-trimester screening?
First-trimester screening is generally not covered by public health insurance. It is considered an “IGeL” service. Despite the requirement to pay out-of-pocket, many pregnant women opt for the screening, even when there are no age-related risk factors present.
Conclusion: Non-invasive, but not always conclusive
First-trimester screening can be performed to assess the risk of various disorders, malformations, and diseases. It is a non-invasive method, so the test is not associated with a risk of miscarriage. At the same time, however, it “only” identifies risks. A definitive diagnosis cannot be made using this method.
The identified risks can be used to optimize further prenatal care. In cases of increased risk—for example, for chromosomal abnormalities—the option of invasive diagnostic testing or cell-free DNA analysis can be considered.
There is currently a discussion about whether cell-free DNA analysis will be covered by health insurance under certain circumstances. If there is an increased risk of pregnancy-induced hypertension, daily aspirin use is considered.
An increased risk is always a source of stress for parents. Therefore, they should always discuss how to handle the results before undergoing first-trimester screening.
